A portable media device can store media assets, such as audio tracks, video tracks or photos that may be played or displayed on the portable media device. Examples of portable media devices are the iPod™ and the iPhone™ portable media devices, which are available from Apple Inc. of Cupertino, Calif., assignee of the present application. A portable media device can acquire media assets, e.g., from a host computer that also serves to enable a user to manage media assets stored on the host computer and/or the portable media device. As an example, the host computer may execute a media management application to manage media assets. One example of a media management application is iTunes®, produced by Apple Inc.
A portable media device typically includes one or more connectors or ports that may be used to interface with other remote devices. For example, the connector or port may enable the portable media device to couple to a host computer, be inserted into a docking system, or receive an accessory device. In the case of the iPod™, for example, a vast array of accessory devices have been developed that may interconnect to the portable media device. For example, an accessory that may be connected to the connector or port can receive commands from a remote control device (e.g., using infrared or other wireless signaling techniques) and send corresponding commands via the connector or port to the portable media device, thereby allowing the user to remotely control the portable media device. As another example, an automobile may include a connector, and the portable media device may be inserted onto the connector such that an automobile media system may interact with the portable media device, thereby allowing the media content on the portable media device to be played using the automobile media system. In another example, a digital camera may be connected to the portable media device to download images and the like.
Portable media devices commonly connect with accessory devices for playback or presentation of tracks stored on the portable media device. A user may want to dock a portable media device to an audio amplification system such as, for example, a home stereo system and play back a video presentation stored on the portable media device. The user desires to experience a video display on the portable media device but have an audio experience provided by the home stereo system. The user expects an isochronous experience, where the audio portion of the presentation is synchronized with the video portion. However, each instance of an audio amplification system may propagate a digital audio input with different delay characteristics, and the delay characteristics may vary depending on characteristics (such as sampling rate) of the digital audio input. Many existing audio/video presentation systems require extensive user interaction in a setup process to interactively input to the system the user's perception of delay between video and audio in response to test signals, allowing the system to compensate for delay. Such setup processes are time consuming and are usually imprecise.
It would therefore be desirable to provide an isochronous audio and video presentation without requiring extensive user interaction.